Biological re-colonization of sub-aerial boundaries of an ‘artificial construction-niche’ contaminated by iron mine tailings: laboratory bioassays

The ability of colonizer organisms to tolerate high metal concentrations is important to the restoration and rehabilitation of mining sites. We investigated colonization on modular cellular surfaces—artificial construction-niche—prepared by combining different proportions of iron mine tailings (8% tailing dam material), soil (90%), and cement (2%) through bioassays conducted under stable laboratory conditions of humidity, temperature, and light intensity. The establishment of microorganisms was measured using CO₂-respirometry and microbiological assays. Sub-aerial communities grown on the experimental materials were composed of heterotrophic and phototrophic macro- and microorganisms. Four groups of phototrophic species were observed: cyanobacteria, algae, mosses, and ferns. The cyanobacteria comprised three genera: Phormidium sp., with branched filaments, Nostoc sp. and Pseudanabaena sp.; algae included Trentepohlia sp. (Chlorophyceae), a sub-aerial or terrestrial green algae. Macroscopic fungal hyphae were also observed. CO₂ production occurred in all cellular modules due to the growth of bacteria, actinobacteria, and fungi. The presence of living organisms on these artificial construction-niche containing iron ore tailings was a promising finding as those colonizers could initiate the processes of primary succession and occupy significant portions of the sub-aerial surfaces, thus actively participating in weathering and soil formation to create new ecological niches for recuperating ironstone outcrop ecosystems.